Submitted to: International Society For Trace Elements Research In Humans
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/2001
Publication Date: 10/1/2001
Citation: Roughead, Z.K., Zito, C., Hunt, J.R. Calcium inhibits heme iron absorption primarily by reducing initial mucosal uptake. 2001. Journal of Trace Elements in Experimental Medicine. v.14. p.320-321.
Technical Abstract: It is hypothesized that calcium inhibits iron absorption by reducing the serosal transfer of heme and nonheme iron. We tested the effects of calcium on heme and nonheme iron absorption by combining gastrointestinal lavage and whole body counting methodologies. Healthy volunteers (n=15) consumed a test meal (wheat muffin, eggs, Canadian bacon, shredded wheat, milk and tea), labeled with the radiotracers Fe-59 (nonheme) and Fe-55 (heme), and served with and without a calcium supplement (448 mg as citrate), 6 wk apart, in a randomized cross-over design. Eight hours after each meal, the gut was cleansed with an oral isosmotic/isotonic solution containing polyethylene glycol. The initial uptake of nonheme iron was determined by comparing the amount of Fe-59 in the body after the lavage procedure to the dose, both measured by whole body counting. The initial uptake of heme iron was determined from the ratio of Fe-59 to Fe-55 in the dose and in the lavage excreta and the initial uptake of nonheme iron. Nonheme and heme iron absorptions were determined 2 wk later by whole body counting and isotopic analyses of blood. Serosal transfer index was calculated as absorption divided by initial uptake, both expressed as % of dose. Data are geometric means (-/+ SD). Consuming a calcium supplement with a low iron bioavailability meal reduced the initial uptake of heme iron by 22% and its absorption by 28%, but did not affect its serosal transfer index. The initial uptake and absorption of nonheme iron from the meal were very low (~2% and ~0.5%, respectively) and were not significantly affected by calcium. In conclusion, calcium supplements consumed with a low iron bioavailability meal interfere with heme iron absorption primarily by reducing its initial mucosal uptake.